Rope and method of making same

ABSTRACT

A plurality of filaments of polyolefin are formed into a strand by twisting. The twisted strand is heat set and then twisted with other strands to form a rope which retains its tensile strength and reduces elongation.

United States Patent 1191 Qarranm et a]. Oct. 8, 1974 [54] ROPE AND'METHOD OF MAKING SAME 2,400,181 5/1946 Warren 57 140 R r 2,971,321 2/1961 Himmelfarb et al... 57/140 R x [75,] Inventors: 4 Carmma1 3,201,930 8/1965 Stirling 57 160 x 8 Pem, Hialeah, both of 3,298,165 1/1967 A1156 57/34 11s [73] Asslgnee: 22: gg Corpmanqn Primary ExaminerD0nald E. Watkins Attorney, Agent, or Firm-Cushman, Darby & [22] Filed: May 10, 1972 Cushman 21 Appl. No.; 252,115

52 111.5. (211 57 140 R, 57/157-TS [57] ABSTRACT 3223 i 2 A plurality of filaments 0f Poll/olefin are formed into a 1 2 1 R Strand The Strand iS heat Set and TS 5 MS S then twisted with other strands to form a rope which retains its tensile strength and redluces elongation. [56] References Cited UNITED STATES PATENTS 8 Clam, 3 D'awmg F'gures 2,343,892 3/1944 Dodge et al 57/140 R ROPE AND METHOD OF MAKING SAME This invention relates to a cordage product and a process for making it, and more particularly to a new synthetic polypropylene and/or polyethylene rope product and a process for its manufacture from polyethylene and/or polypropylene filaments.

Rope is produced from vegetable and synthetic fibers. In the case of continuous filament rope products made from synthetic polymers, particularly polypropylene and polyethylene filaments, the rope is made in three stages. First, a yarn is made by twisting together a bundle of fibers, this step imparting the primary twist. Two or more yarns are then twisted together in the opposite direction from the primary twist, to make a strand and several strands are twisted together to make the rope.

The first step, that is the step of imparting a primary twist to the yarn, has been considered a necessary step because polypropylene and polyethylene fibers are very stiff and have low memory, tending to unravel, and come fully apart in the subsequent operations of making the strands, and on closing the strands to make the final rope products. The primary twist helps the strands to remain firm, and a satisfactory rope product is produced. However, imparting primary twist to the synthetic polypropylene and polyethylene yarn constitutes an expensive manufacturing step, and creates a requirement for expensive equipment. It is an object of the present invention to provide a process for manufacture of novel and improved synthetic polypropylene and polyethylene rope products, without the necessity of introducing a primary twist to the yarns. The process is simple, fast and much less expensive than the conventional process in which a primary twist is imparted to the yarn.

In accordance with the present invention, a bundle of filaments, without any twist having been imparted previously, is twisted into a strand, e.g. on a conventional former rope machine. As the strands are being made the twist imparted into the strand is heat set before thenext step, preventing further unraveling during the subsequent operation of closing the strands into a rope product.

The invention may be applied to filaments of polyolefin, especially filaments of polyethylene, polypropylene, or blends thereof, and copolymers of ethylene and propylene. The filaments may be melt spun and may have any cross-section, including round, square and the like. They also may be ribbons severed from films, and

may be blown filaments of the kind described in U.S. Pat. No. 3,3 l5,454. The filaments ordinarily'will be ori ented for strength in the conventional manner.

In general the filaments will be about 65 to 1,650 denier. The strands made by twisting bundles of filaments will be 22,500 to 1,080,000 deniers, and the rope may be 67,500 to 3,240,000 deniers. The number of strands in the rope will vary according to the size of rope desired.

The invention will be better understood from the following detailed description of preferred embodiments, reference being made to the drawing, in which:

FIG. 1 is a schematic view, showing the formation of untwisted filaments and temporary winding of them in packages in preparation for use in the process of the present invention;

be stretched and otherwise processed in conventional manner. The wind-up step at this stage is not essential,

as the filaments can proceed directly to the strandforming step. However, it provides a convenient way to accumulate filaments to be combined in a single strand.

FIG. 2 illustrates formation of a strand from three packages 3 of filaments. The filaments are wound from the packages through a guide 4 and a conical former 5. At this stage, no twist has been imparted, but the fila ments are formed into a compact bundle by the former 5. I he filaments then move one or more times around capstan rollers 6 and 7 and onto a spool 8, of a conventional rope making machine, e.g. at a speed of 50-250 feet per minute. The rollers 6 and 7 and the spool 8 are mounted on a frame 9 which rotates about a horizontal axis while the rollers and the spool rotates about their own axis, the spool winding up the strand. This causes a twist to beimparted to the strand. This twist depends upon the final diameter of the rope to bemade, but may be l-l2 turns per inch.

A radiant heater 10 is mounted adjacent the spool 8, to apply heat to the twisted strand as it winds onto the spool and to the outer layer of the strand wound on the spool. To improve heat transfer, there is a forced air blower l1 behind the heater, which blows air over the heater and onto the spool. The heater raises the temperature of the strand sufficiently to heat set it. This step compacts the structure, which thereafter retains a firm twist during the final operation.

The temperature to which the fibers are heated in this step may be controlled by a thermostat which measures the strand temperature or the temperature of the air passing over the heater, and which regulates the power applied to the infrared heaters and/or the operation of the blower. The temperature should be controlled to be lower than the softening point of the filaments, but higher than about F. The melting point of polypropylene is about 330F and the heat set temperature can be as low as about I230F. The optimum temperature is about 280F. In the case of polyethylene, the optimum temperature is about 210, or 212F. The melting point is about 260F' and the lowest temperature is about 160F. As the temperature is lowered in either case, consistency is reduced somewhat, although, because of the long storage of the heated strands in accordance with the present invention, somewhat lower temperatures can be used. Once the strand is heated to this temperature and'wound on the spool, it will maintain the temperature for a considerable period of time, providing for thermalequilibrium to be achieved before the strand is used in the next as in FIG. .2, i.e., having a spool 12 and capstan rollers 13 and 14. However, no further heat setting is necessary. A twist of l to 5 turns per inch may-be used.

The rope, when made in this way, is resistant to detwisting. Since the process achieves this result without the primary twist, the cost of manufacture is substantially reduced.

The following example illustrates the process, it being understood that no limitation thereto is intended.

Twelve mil polypropylene filaments are extruded and 25 ends are wound on a tube. Three tubes of these filaments serve as the supply for making of a strand.

However, it will be understood that the number of tubes to be used as the supply for this operation will depend on the diameter of the intended rope product, i.e. to obtain a A. inch diameter three-strand polypropylene rope it will be necessary to have three tubes of 25 ends each of 12 mils polypropylene filament, that is 75 filaments per strand. That is, three strands of this type, closed together, will make a Mr inch diameter polypropylene rope.

The filaments on each roll are withdrawn from the supply tubes at a speed of 120 feet per minutes, passing through a guide and a die to a pair of capstans to impart a twist of 3 turns per inch to the strand, which is fed onto a spool. As the strand was wound onto the spool, it was subjected to infra-red rays from a radiant lamp at the temperature of 280F, to heat set the twist in the strand. The resulting heat set strands are found to retain the twist firmly and satisfactorily for subsequent operations. Three of them are closed on a conventional rope making machine into a inch diameter polypropylene rope, with the same tensile strength as it would have had if made from a composite of primary twisted yarns, with the added advantage of a reduction of its ultimate elongation.

Although the invention has been described in detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. The method of forming a stranded rope structure which comprises twisting a plurality of untwisted filaments of a member of the group consisting of polyethylene, polypropylene and copolymers of ethylene and propylene, to form a strand, heat setting the strand and twisting a plurality of the resulting strands into a rope which retains its tensile strength and at the same time reduces the ultimate elongation of the rope.

2. The method according to claim 1 in which the twisted strand is wound onto spool and heat set by heating the strand as it is being wound onto the spool.

3. A method according to claim 2 in which the heated, twisted strand is stored on said spool until it has cooled, before being made into a rope.

4. A method according to claim 1 in which the filaments are polypropylene.

5. A method according to claim 1 in which the twisted strand is wound onto a spool and heat set by radiant heat directed against the strand as it approaches the bobbin and against the strand wound on the bobbin.

6. A method according to claim 5 including blowing heated air against the strand while radiant heat'is directed against it.

7. Polyolefin rope made by the method of claim 1.

8. The method of forming a stranded rope structure which comprises twisting together, I to 12 turns per inch, sufficient untwisted 65 to 1,650 denier filaments of a member of the group consisting of polyethylene, polypropylene and copolymers of ethylene and propylene, to form a strand of 22,500 to 1,080,000 denier, heat setting the strand, and twisting a sufficient number of the resulting strands l to 5 turns per inch, into a rope of 67,500 to 3,240,000 denier. 

1. THE METHOD OF FORMING A STRANDED ROPE STRUCTURE WHICH COMPRISES TWISTING A PLURALITY OF UNTWISTED FILAMENTS OF A MEMBER OF THE GROUP CONSISTING OF POLYETHYLENE, POLYPROPYLENE AND COPOLYMERS OF ETHYLENE AND PROPYLENE, TO FORM A STRAND, HEAT SETTING THE STRAND AND TWISTING A PLURALITY OF THE RESULTING STRANDS INTO A ROPE WHICH RETAINS ITS TENSILE STRENGTH AND AT THE SAME TIME REDUCES THE ULTIMATE ELONGATION OF THE ROPE.
 2. The method according to claim 1 in which the twisted strand is wound onto spool and heat set by heating the strand as it is being wound onto the spool.
 3. A method according to claim 2 in which the heated, twisted strand is stored on said spool until it has cooled, before being made into a rope.
 4. A method according to claim 1 in which the filaments are polypropylene.
 5. A method according to claim 1 in which the twisted strand is wound onto a spool and heat set by radiant heat directed against the strand as it approaches the bobbin and against the strand wound on the bobbin.
 6. A method according to claim 5 including blowing heated air against the strand while radiant heat is directed against it.
 7. Polyolefin rope made by the method of claim
 1. 8. The method of forming a stranded rope structure which comprises twisting together, 1 to 12 turns per inch, sufficient untwisted 65 to 1,650 denier filaments of a member of the group consisting of polyethylene, polypropylene and copolymers of ethylene and propylene, to form a strand of 22,500 to 1,080,000 denier, heat setting the strand, and twisting a sufficient number of the resulting strands 1 to 5 turns per inch, into a rope of 67,500 to 3,240,000 denier. 